A browser engine (also known as a layout engine or rendering engine) is a core software component of every major web browser. The primary job of a browser engine is to transform HTML documents and other resources of a web page into an interactive visual representation on a user's device.

Name and scope

A browser engine is not a stand-alone computer program but rather a critical piece of a larger program, such as a web browser, from which the term is derived. The word "engine" is an analogy to the engine of a car.

Besides "browser engine", two other terms are in everyday use regarding related concepts: "layout engine" and "rendering engine".[1][2][3] In theory, layout and rendering (or "painting") could be handled by different engines. In practice, however, a given browser engine's rendering and layout components are tightly coupled and rarely encountered on their own outside the browser engine, unlike the case with browsers' scripting engines.

In addition to layout and rendering, a browser engine enforces the security policy between documents, handles navigation through hyperlinks and data submitted through forms, and implements the Document Object Model (DOM) exposed to scripts associated with the document.

Every significant web browser supports JavaScript (JS) to enable a wide range of interactive behavior specified by the publisher. However, JS language support is treated as a separate concern, and browser vendors use a dedicated JavaScript engine to parse and evaluate it.[4] Although JS was initially created as a simple language for use on web pages, it became a general-purpose language used elsewhere. Browsers have sophisticated methods of coordinating their engines.[1][5]

Browser engines are used in other types of programs besides web browsers. For example, an email client might rely on a browser engine for displaying HTML email. The Electron framework, powered by Blink and V8 from Google's Chromium project, enables software developers to use technologies first created for the web platform—such as HTML, CSS, JavaScript, and the DOM—to create graphical desktop applications. Developer familiarity browser-based technologies has resulted in Electron and other cross-platform, browser engine-based application frameworks often being used in lieu of traditional GUI toolkits.

Layout, style, and rendering

The layout of a web page is typically specified by Cascading Style Sheets (CSS). Each style sheet is a series of rules which the browser engine interprets to determine how the document should be presented. For example, a published web page might use CSS to specify rules to style typography details, such as font, color, and text size. The engine combines all relevant CSS rules to calculate the concrete graphical coordinates for the visual representation it will paint on the screen.[1][5]

Some engines may begin rendering before a page's resources are downloaded. This can result in visual changes as more data is received, such as images being gradually filled in or a flash of unstyled content.

Notable engines

Timeline

Only the duration of active development is shown, which is when relevant new Web standards continue to be added to the engine.

See also

References

  1. 1 2 3 "Behind the scenes of modern web browsers". Tali Garsiel. Retrieved 21 April 2018.
  2. 1 2 "Gecko". Mozilla. Archived from the original on 4 June 2014. Retrieved 21 April 2018.
  3. ↑ "Introducing Goanna". M.C. Straver. 22 June 2015. Retrieved 21 April 2018.
  4. ↑ Bak, Lars (29 April 2009). "Inside V8—A Javascript Virtual Machine" (Interview). Interviewed by Meijer, Erik; Torre, Charles. Microsoft. Retrieved 3 July 2020.
  5. 1 2 "What Every Frontend Developer Should Know About Webpage Rendering". Retrieved 1 December 2023.
  6. ↑ Paul Festa (14 January 2003). "Apple snub stings Mozilla". CNET Networks. Archived from the original on 25 October 2012. Retrieved 16 February 2017.
  7. ↑ "Open-sourcing Chrome on iOS!". 2017. Retrieved 26 April 2021. Due to constraints of the iOS platform, all browsers must be built on top of the WebKit rendering engine.
  8. ↑ Bright, Peter (3 April 2013). "Google going its way, forking WebKit rendering engine". Ars Technica. Conde Nast. Retrieved 9 March 2017.
  9. ↑ Mackie, Kurt (10 December 2018). "Microsoft Edge Browser To Get New Rendering Engine but EdgeHTML Continues". Redmond Mag. Retrieved 21 December 2019.
  10. ↑ Mendelevich, Alan (14 May 2021). "You Think You Can Forget About the "Legacy" Microsoft Edge? Not So Fast!".
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